Practice talking out loud. Practice breathing. Communicate with your teacher/counselor so they know about your stutter. If your teacher wants you to speak in front of class (which I think is a good, hard opportunity for life) then request advance notice. Preferably, you'd have something pre-written you practiced at home so you can do your best in front of the class. Anxiety and fear will always be with us, the best you can do is prepare and be brave.